Heater cables, such as self-regulating heater cables, tracing tapes, and other types, are cables configured to provide heat in applications requiring such heat. Heater cables offer the benefit of being field-configurable. By this, heater cables may be applied or installed as needed without the requirement that application-specific heating assemblies be custom-designed and manufactured, though heater cables may be specifically designed for application-specific uses in some instances.
In some approaches, a heater cable operates by use of a pair or more of bus wires having a high conductance coefficient (i.e., low resistance). The bus wires are coupled to differing voltage supply levels to create a voltage potential between them. A positive temperature coefficient (PTC) material is often situated between the bus wires and current is allowed to flow through the PTC material, thereby generating heat. As the temperature increases, so does the resistance of the PTC material, thereby reducing the current therethrough and the heat generated. The heater cable is thus self-regulating in terms of the amount of thermal energy (i.e., heat) output by the cable.
Certain configurations of previous heater cables may suffer high temperature gradients throughout the cable. Such gradients can occur lengthwise along the length of the cable or can occur across a cross-section of the cable. These high temperature gradients may be caused by small high-active heating volumes (e.g., PTC material) within the heater cable that can create localized heat as opposed to heat spread over a larger surface area or volume. In some instances, these localized high-active heating volumes can cause non-uniform heat output along the length or across the width of the cable. Furthermore, the localization of increased thermal output may generate heat of a temperature that can reduce the lifespan of the heater cable or can thermally age some portions of the heater cable quicker than others. A heater cable that reduces temperature gradients may be desirable in some instances.